1. Field of the Invention
The present invention relates to a device for ultrasonically imaging and diagnosing the peripheral part of a cavity of a human body, said device having an ultrasonic wave transmitting and receiving section and being inserted into the body cavity to form ultrasonic sectional images of organs in the body cavity.
2. Description of the Related Art
The conventional ultrasonic image devices are well known as those having an endoscope into which the ultrasonic wave transmitting and receiving section is incorporated. The ultrasonic image devices of this kind are generally grouped into the ones of the electronic scan type and the others of the mechanical type, depending upon the manner of scanning the body cavity with ultrasonic beam applied from the ultrasonic wave transmitting and receiving section. In the case of the device of the mechanical scan type, the rotating force of the drive means such as the motor located at the endoscope operating section is transmitted to the ultrasonic wave transmitting and receiving section in the front end of the inserting section through a flexible drive shaft (or coil shaft) in the inserting section of the endoscope, so that the ultrasonic wave transmitting and receiving section can be rotatingly driven. Further, a signal received by the ultrasonic wave transmitting and receiving section is transmitted to a signal receiving circuit at the endoscope operating section through a signal cable passed through the flexible drive shaft in the inserting section.
An ultrasonic signal received by the ultrasonic wave transmitting and receiving section is quite faint and it is easily affected by noises caused by the light source for the endoscope and by the video camera located outside.
In order to solve this problem, the outer or external conductive line of the signal cable which is of the coaxial type i made low in electric resistance and it is also arranged that a single line is used in the signal cable and that the flexible drive shaft which is made by a metal coil and through which this signal cable is passed serves as the outer conductive line.
However, the signal cable and the coil shaft in the ultrasonic image device must be small in diameter, flexible, and good in curving durability. Therefore, the diameter of the outer conductive line and its material must be limited in the case of the signal cable and its diameter and material (stainless steel) must also be limited in the case of the coil shaft. This cause both of them to have high values in electric resistance. In addition, the inserting section through which both of them are passed is long, and they must be made extremely long according to the length of the inserting section. This also causes the outer conductive line of the signal cable and the coil shaft to become high in electric resistance, thereby making it unsatisfactory to shield noises outside.
In the case of the device of the electronic scan type, a solid pickup element and the ultrasonic wave transmitting and receiving section become sources for causing noises and they interact with each other to add undersirable influence to each other. When an electric process means such as the high frequency processor is used together with them, therefore, they are likely to be undesirably influenced by noises outside.